Method for determining structural parameters of composite building panels

ABSTRACT

A method of determining face paper properties of all types of wallboard including providing a core strength value of the wallboard, determining a required nail pull value based the wallboard specifications and calculating a face paper stiffness value based on the provided core strength value and the determined nail pull value. The method includes displaying the calculated face paper stiffness value on a display device.

PRIORITY CLAIM

This application is a continuation-in-part application of U.S. patentapplication Ser. No. 12/544,707 filed on Aug. 20, 2009, now U.S. Pat.No. 8,204,698.

FIELD OF THE INVENTION

This invention relates to composite building panels. More specifically,it relates to a method for determining structural parameters of gypsumwallboard.

BACKGROUND OF THE INVENTION

Composite building panels, such as gypsum wallboard, are well known forinterior wall and ceiling construction. Some of the main advantages ofwallboard over other materials is that wallboard is less expensive, afire retardant and easy to work with in construction applications. Inconstruction, wallboard is typically secured to wood or metal supportsof framed walls and ceilings using fasteners such as nails or screws.Because wallboard is relatively heavy, it must be strong enough toprevent the fasteners from pulling through the wallboard and causing thewallboard to loosen or fall away from the supports.

Nail pull is an industry measure of the amount of force required forwallboard to be pulled away from the associated support and over thehead of such a fastener. Preferable nail pull values for wallboard arein the approximate range of between 65-85 pounds of force. Nail pull isa measure of a combination of the wallboard core strength, the facepaper strength and the bond between the face paper and the core. Nailpull tests are performed in accordance with the American Society forTesting Materials (ASTM) standard C473-00 and utilize a machine thatpulls on a head of a fastener inserted in the wallboard to determine themaximum force required to pull the fastener head through the wallboard.Because the nail pull value is an important measure of wallboardstrength, minimum required nail pull values have been established forwallboard. Accordingly, manufacturers produce wallboard that meets orexceeds the minimum required nail pull values.

To ensure that wallboard meets the required nail pull values,conventional wallboard manufacturers adjust the structural parameters ofthe wallboard. Specifically, manufacturers typically adjust the facepaper weight of wallboard or the weight of the wallboard to meet therequired nail pull value, depending on the economics of the process.During manufacturing, wallboard is tested to determine if it meets therequired nail pull value. If the tested nail pull value of the wallboardis less than the required nail pull value, manufacturers increase theface paper weight on the wallboard and/or the weight of the wallboard.This process is iterated until the required nail pull value is met.

Such a process is inaccurate and commonly causes the tested nail pullvalues to exceed the required nail pull values due to excess face paperweight and/or overall board weight added to the wallboard. Also, theexcess weight from the face paper and/or from the core to wallboard andthereby increases manufacturing and shipping costs of wallboard.Further, there is the likelihood of wasting time and material until thedesired nail pull values are achieved on the wallboard production line.

Thus, there is a need for an improved technique of adjusting wallboardmanufacturing systems to produce wallboard that meets specified nailpull values.

SUMMARY OF THE INVENTION

These, and other problems readily identified by those skilled in theart, are solved by the present method of determining structuralproperties of composite building panels such as wallboard.

The present method is designed for determining structural parameters ofgypsum wallboard prior to manufacturing to reduce manufacturing andshipping costs as well as significantly reduce manufacturing time.

More specifically, the present method determines structural parametersof wallboard and includes providing a core strength value of thewallboard, determining a required nail pull value and calculating a facepaper stiffness value based on the provided core strength value and thedetermined nail pull value. The calculated face paper stiffness value isdisplayed on a display device for use by a manufacturer.

In another embodiment, a method of manufacturing wallboard includesdetermining a required nail pull value, providing a core strength valueof the wallboard and determining a face paper stiffness value based onthe required nail pull value and the provided core strength value. Themethod includes determining a face paper weight based on the determinedface paper stiffness value, selecting a face paper type based on thedetermined face paper weight and producing the wallboard using theselected face paper type and the provided core strength value.

Determining the structural parameters prior to manufacturing enablesmanufacturers to save significant manufacturing and shipping costs byeliminating excess face paper weight or wallboard weight that istypically utilized for the wallboard to meet required nail pull values.Additionally, a significant amount of manufacturing time is savedbecause less time is needed to test the manufactured wallboard todetermine the composite design and weight of the final product needed tomeet required nail pull values. Furthermore, the structural integrityand strength of wallboard is maintained, even though the additionalweight and stress added by the excess face paper is reduced.

DETAILED DESCRIPTION OF THE DRAWINGS

FIG. 1 is a table illustrating a comparison between measured nail pulldata and predicted nail pull data for different types of wallboard usingdifferent face paper stiffness values from various face paper weightsand Tensile Stiffness Index Area (TSIA) as well different core strengthvalues at various board densities.

FIG. 2 is a graph illustrating nail pull as a function of the face paperstiffness at different core strength values at a board density of 37lb/ft³.

FIG. 3 is a graph illustrating nail pull as a function of the corestrength at different face paper stiffness values at a board density of37 lb/ft³.

FIG. 4 is a graph illustrating the relationship between the face paperstiffness and the core strength at different required nail pull valuesat a board density of 37 lb/ft³.

FIG. 5 is a graph illustrating the relationship between the face paperweight and the Tensile Stiffness Index Area values needed to achieve arequired nail pull value of 77 lb_(f) at different core strength valuesfor 37 lb/ft³ board density.

FIG. 6 is a table identifying certain face paper weight values andTensile Strength Index Area (TSIA) values needed to achieve a requirednail pull value of 77 lb_(f) at different core strength values for 37lb/ft³ board density based on the graph of FIG. 5.

DETAILED DESCRIPTION OF THE INVENTION

Nail pull values are critical to the strength and usefulness of gypsumwallboard. If a nail pull value for a particular wallboard is too low,the fastener holding the wallboard on a frame or other support can pullthrough the wallboard and cause the wallboard to crack, break or fallfrom the frame or support. Alternatively, if nail pull values are toohigh (i.e., significantly exceed required nail pull values), wallboardproduction resources are inefficiently applied and money is wastedduring manufacturing.

A problem in gypsum wallboard manufacturing is how to accuratelydetermine the face paper weight that correlates to a required nail pullvalue for wallboard and a way that more efficiently utilizesmanufacturing and shipping costs, as well as manufacturing time. Asstated above, wallboard manufacturers perform tests on wallboard todetermine if it meets a required nail pull value. If the required nailpull value is not met, manufacturers typically increase either the facepaper weight of the wallboard and/or the board weight. These steps arerepeated until the required nail pull value of the wallboard is met.This process is not accurate and often causes the wallboard to haveexcess face paper weight or board weight, and thereby increasesmanufacturing and shipping costs as well as manufacturing time.

Previous nail pull model correlates the nail pull of gypsum boards tothe face paper stiffness value and the core strength value for smallergypsum boards (half inch gypsum boards). In another embodiment, thisnail pull model has been expanded to a generalized nail pull model thatcorrelates the nail pull value with the face paper stiffness value andthe core strength value of several different types of gypsum boardsincluding, but not limited to, half inch gypsum boards, three-quarterinch gypsum boards and lightweight gypsum boards.

Specifically, the generalized nail pull model below relates the nailpull value to the face paper stiffness value and the core strength valueof gypsum boards having a density from 28 to 48 lb/ft³.

The generalized nail pull model can be used to determine a face paperstiffness value for wallboard prior to manufacturing that meets therequired nail pull value. The method utilizes Equation (1) below tocorrelate a required nail pull value with the face paper stiffness valueand the core strength value of wallboard. Equation (1) is as follows:Nail Pull(lb_(f))=a+(lb_(f))+[b(lb_(f)/(kN/m))×(face paperstiffness(kN/m))]+[c×Ilb_(f)/psi)×(core strength(psi))]  (1)where b=0.009490606731 and c=0.073937419 are constants determined fromtesting data that best fit the data shown. The constant “a” isdetermined based on Equation (2) as follows:a=a1+a2/[1+Exp(−(board density−a3)/a4)]  (2)where a1=67441271, a2=20.870959, a3=43.718215 and a4=2.1337464, and theboard density is determining using:Board density=board weight/board caliper  (3)FIG. 1 shows the predictions of the nail pull from the generalized nailpull model as comparing to the measured nail pull using different typesof board samples at a specific board density with various face paper andcore strength.

In some situations, changing the face paper stiffness is moreeconomically feasible. Prior to manufacturing, the required nail pullvalue for the wallboard at a target weight and caplier is specified(i.e., half inch, light weight, five-eight inch etc.). These values areentered in Equation (1) above to determine the face paper stiffnessvalue of the wallboard. For example, for board density of 37 pounds percubic feet, Equation (1) becomes:Nail Pull(lb_(f))=7.602932(lb_(f))+[0.009490606731(lb_(f)/(kN/m))×(facepaper stiffness(kN/m))]+[0.073937419(lb_(f)/psi)×(core strength (psi))]

The face paper stiffness value for wallboard having a board density of37 lb per cubic ft is determined using a core strength value of 450pounds per square inch (psi) and a required nail pull value of 77pound-force (lb_(f)) as follows:77 lb_(f)=(7.602932(lb_(f)))+[(0.009490606731(lb_(f)/(kN/m)))×(facepaper stiffness(kN/m))]+[(0.073937419(lb_(f)/psi))×(450 psi)]where the face paper stiffness value=3805.37 kiloNewton/meter (kN/m).

The face paper stiffness value is a product of the face paper weight andthe Tensile Stiffness Index Area (TSIA) value as shown in the followingequation:Face Paper Stiffness(kN/m)=Face Paper Weight(g/m²)×TSIA(kNm/g)  (2)

Using the above example, the Face Paper Weight for the above wallboardhaving a core strength value of 450 psi, a required nail pull value of77 lb_(f) and a TSIA of 18 kiloNewton-meter/gram (kNm/g) is as follows:

$\begin{matrix}{{{Face}\mspace{14mu}{Paper}\mspace{14mu}{Weight}\mspace{11mu}\left( {g\text{/}m^{2}} \right)} = {{Face}\mspace{14mu}{Paper}\mspace{14mu}{Stiffness}\mspace{11mu}{\left( {{kN}\text{/}m} \right)/}}} \\{{TSIA}\mspace{11mu}\left( {{kNm}\text{/}g} \right)} \\{= {\left( {3805.37\mspace{14mu}{kN}\text{/}m} \right)/\left( {18\mspace{14mu}{kNm}\text{/}g} \right)}} \\{= {211.41\mspace{14mu}{gram}\text{/}{meter}\mspace{14mu}{squared}\mspace{11mu}\left( {g\text{/}m^{2}} \right)}} \\{= {43.3\mspace{14mu}{{lb}/1000}\mspace{14mu}{ft}^{2}}} \\{= {43.3\mspace{14mu}{{lb}/{MSF}}}}\end{matrix}$

In the above equation, the TSIA value is a measurement of the normalizedface paper stiffness prior to the production. Specifically, anultrasonic Tensile Stiffness Orientation (TSO®) tester machine measuresthe Tensile Stiffness Index (TSI) in all directions of the face paper todetermine the TSIA. The stiffer the face paper, the larger the TSIAvalues. The approximate range of TSIA values for wallboard is 12 to 26kNm/g.

The face paper stiffness value and TSIA value are used to determine theweight of the face paper that is needed to achieve the required nailpull value for wallboard having a designated core strength value at aspecific board density. The calculation for determining the face paperweight is therefore a two-step process of first determining the facepaper stiffness and then determining the face paper weight for thewallboard being manufactured.

Equations (1), (2), and (3) are preferably stored in a memory of acomputer, personal data assistant or other suitable device. The requirednail pull values, core strength values and constants are also stored inthe memory in a database or other searchable data format. The memory maybe a read-only memory (ROM), random access memory (RAM), compact diskread-only memory (CD ROM) or any other suitable memory or memory device.A user or manufacturer inputs the required nail pull value anddesignated core strength value for the specific wallboard product intothe computer using a keyboard or other suitable input device.Alternatively, the required nail pull value and designated core strengthvalue for the wallboard may be downloaded and stored in a file or folderin the memory. A processor, such as a microprocessor or a centralprocessing unit (CPU), calculates the face paper weight for thewallboard using Equations (1), (2), and (3), the inputted nail pullvalue and the inputted core strength value. The calculated face paperweight, or alternatively the face paper stiffness value, is displayed toa user on a display device such as a computer screen, monitor or othersuitable output device or printed out by a printer. The user uses thecalculated face paper weight to select the face paper or face paper typethat is to be adhered to the core during manufacturing of the wallboard.The face paper selected using the present method typically targets theface paper stiffness and weight needed to achieve the required nail pullvalue compared to conventional wallboard production techniques.Additionally, the present method reduces the overall weight of themanufactured wallboard, which reduces manufacturing and shipping costs.The present method also significantly reduces the manufacturing timeassociated with producing the wallboard because the intermediate testingof the wallboard to determine if the wallboard meets required nail pullvalues is no longer necessary.

FIG. 1 is a table that illustrates a comparison between the measurednail pull data and the predicted nail pull data for different wallboardusing Equation (1). As shown in the table, the predicted average nailpull data using Equation (1) correlates well with the tested or measuredaverage nail pull data of the wallboard. Equations (1), (2), and (3) canalso be used to predict different structural parameters or values ofwallboard to enhance the manufacturing process.

For a board density of 37 lb/ft³, from Equation (1), nail pull data inEquation (1) can be expressed as a linear function of the face paperstiffness at different core strength values ranging from 200 psi to 800psi, as shown in FIG. 2. The core strength value of wallboard variesbased on the type of wallboard being manufactured. The typical range ofcore strength values for the wallboard considered in FIG. 1 is 300 to800 psi.

The nail pull data can also be plotted as a linear function of the corestrength with the face paper stiffness values ranging from 2000 kN/m to5000 kN/m, as shown in FIG. 3. Preferably, the face paper stiffnessvalues range from 3000 to 5000 kN/m for wallboard. In FIGS. 2 and 3, itis apparent that increasing either the face paper stiffness value or thecore strength value of wallboard increases the nail pull value.

FIG. 4 shows a plot of the face paper stiffness value as a function ofthe core strength value at various different nail pull values.Specifically, line “A” illustrates the relationship between the facepaper stiffness values and the core strength values at a target minimumnail pull value of 77 lb_(f). Furthermore using Equation (2), a higherface paper stiffness value can be accomplished by increasing either theface paper weight or the TSIA.

FIG. 5 illustrates the relationship between the face paper weight andthe TSIA that meets a required nail pull value of 77 lb_(f). The facepaper weight requirements for different TSIA values are summarized inthe table shown in FIG. 6. Note that increasing the TSIA value from 12to 20 kNm/g tends to reduce the required face paper weight by an averageof 40% at core strength of 450 psi, while maintaining the required nailpull value of 77 lb_(f).

The generalized nail pull model enables a user to determine the optimumface paper sheet weight that meets a designated nail pull value at aspecific core strength value for all types of wallboard, such aswallboard having the following formulations:

Example A

-   -   Stucco: 850-950 lbs per 1000 ft²    -   HRA: 12-16 lbs per 1000 ft²    -   Glass Fiber: 0-2 lbs per 1000 ft²    -   Dispersant (wet basis): 0-8 lbs per 1000 ft²    -   Pre-Gel Corn Flour (dry basis): 20-40 lbs per 1000 ft²    -   STMP (MCM) (dry basis): 2-3 lbs per 1000 ft²    -   Water-to-stucco ratio: 0.8-1.1

Example B

-   -   Stucco: 1100-1300 lbs per 1000 ft²    -   HRA: 8-11 lbs per 1000 ft²    -   Dispersant (wet basis): 0-8 lbs per 1000 ft²    -   Acid-Modified Starch (dry basis): 0-5 lbs per 1000 ft²    -   Pre-Gel Corn Flour (dry basis): 0-10 lbs per 1000 ft²    -   STMP (MCM) (dry basis): 07-1.5 lbs per 1000 ft²    -   Water-to-stucco ratio: 0.7-0.88

Example C

-   -   Stucco: 1800 lbs per 1000 ft²    -   HRA: 5-10 lbs per 1000 ft²    -   Glass Fiber: 4.5-5.3 lbs per 1000 ft²    -   Dispersant (wet basis): 0-12 lbs per 1000 ft²    -   Acid-Modified Starch (dry basis): 4-6 lbs per 1000 ft²    -   Pre-Gel Corn Flour (dry basis): 0-2 lbs per 1000 ft²    -   STMP (MCM) (dry basis): 0-0.7 lbs per 1000 ft²    -   Water-to-stucco ratio: 0.63-0.75

The above embodiments of the present method enable wallboardmanufacturers to determine important parameters and properties of thewallboard prior to manufacturing such as the face paper weight needed toachieve a required nail pull value. Obtaining these parameters prior tomanufacturing helps to significantly reduce manufacturing time, as wellas manufacturing costs and shipping costs. The present method alsoallows manufacturers to maintain the structural integrity andperformance of wallboard without adding face paper weight or overallweight on wallboard.

While several particular embodiments of the present method have beenshown and described, it will be appreciated by those skilled in the artthat changes and modifications may be made thereto without departingfrom the invention in its broader aspects and as set forth in thefollowing claims.

What is claimed is:
 1. A method of manufacturing a wallboard comprising:determining a required nail pull value based on the wallboard type;providing a processor configured to perform the following steps:inputting a core strength value of the wallboard into the processor;determining a face paper stiffness value based on said determinedrequired nail pull value and said provided core strength value;determining a face paper weight based on said calculated face paperstiffness value; selecting a face paper type based on said face paperweight; sending said face paper type and said core strength value to awallboard manufacturing machine; and producing the wallboard with thewallboard manufacturing machine using said selected face paper type andsaid provided core strength value.
 2. The method of claim 1, whereindetermining said face paper stiffness value is based on the followingequation:Nail Pull(lb_(f))=a(lb_(f))+[b(lb_(f)/(kN/m))×(face paperstiffness(kN/m))]+[c(lb_(f)/psi)×(core strength(psi))] whereinb=0.009490606731 and c=0.073937419 and wherein a=a1+a2/[1+Exp(−(boarddensity−a3)/a4)] and wherein a1=6.7441271, a2=20.870959, a3=43.718215and a4=2.1337464.
 3. The method of claim 1, wherein determining saidface paper weight includes dividing said face paper stiffness value by aTensile Stiffness Index Area (TSIA) value.
 4. The method of claim 3,wherein said TSIA value is measured by an ultrasonic tensile strengthorientation tester.
 5. The method of claim 3, wherein said TSIA value isin the range of 12 to 26 kNm/g.
 6. The method of claim 1, which includesstoring at least one of said calculated face paper stiffness value andsaid calculated face paper weight in a memory.
 7. The method of claim 6,wherein said memory includes at least one of: a read-only memory, arandom access memory and a CD ROM.